Polymer materials frequently have solubility in organic solvents and film-forming methods utilizing the solubility have been used in many industrial fields. For example, they are variously developed in different fields, ranging from large-scale fields, such as building coating materials, automobile coating materials, and industrial coating materials, to water-repellant and oil-repellant agents, fiber-treating agents, antireflection films in various fields, such as photographic films, displays, and optical parts, photoresist materials for semiconductor production, bottom reflection films, top reflection films, recording layer coatings, coating-type light guides, magnetic shields, and the like. In general, organic solvents used for coating of polymer compounds are polar solvents and the compounds are put into practical use after facilitating dissolution of the polymers.
As the polymer to be used after film-formation, a fluorine-containing polymer material may be mentioned. In this case, it becomes possible to impart characteristic properties on the uppermost surface in wide application fields of high-tech materials owing to the characteristics of fluorine atoms, such as water repellency, oil repellency, low water absorbability, water resistance, heat resistance, weather resistance, corrosion resistance, transparency, light sensitivity, low refractivity, and low dielectric property. However, since the material is poor in solubility in an organic solvent, a range of selecting solvents to be used is narrow. Therefore, it is known that the fluorine-containing polymer material is frequently applied using a highly polar alcohol or ketone solvent or a homologous perfluorinated solvent (completely fluorinated solvent).
Industrially, there are limitations that it is necessary for the solvent selected to have an appropriate boiling point in order to perform a suitable coating and flash point is required to be as high as possible in order to perform operations safely. On the other hand, in the case of applying it by coating, in a system of using polar solvents, there are cases that the polar solvents are not suitable for practical use depending on the chemical properties of substrate materials and lower-layer films.
As application fields wherein a fluorine-containing polymer material is applied on an upper part of the other polymer material, there may be mentioned a semiconductor-producing field wherein a fluorine-containing protective film or reflection film is formed an upper part of a photoresist before use. Namely, in recent semiconductor industry, resist materials of fluorine-based compounds have been actively studied as novel materials highly transparent to short-wave UV light such as an F2, ArF, or KrF laser and it has been apparent that transparency at the wavelength used is improved by introducing fluorine atom(s). Therefore, in one useful application field of a fluorine-containing polymer, a developing fluid-soluble photoresist reflection film has been used as a top coat. In this case, application of the top coat suppresses roughness and interference of light. Namely, it is important to increase a fluorine content of the top coat film to lower a refractive index. At the same time, it is necessary to devise prevention of erosion of a photoresist surface which becomes a lower layer at coating. Therefore, in a conventional top coat, there has been used a method of solubilizing a low-molecular-weight fluorine-based acidic substance in a salt form in a water-soluble polymer material and applying it in an aqueous solution form on a photoresist film.
On the other hand, an immersion lithography rapidly becomes conspicuous and, in particular, has attracted as a means for prolonging the exposing technology with an ArF excimer laser in the whole industry. In the immersion exposure, since a photoresist surface comes into contact with an immersion medium (e.g., water), it has been proposed to apply a top coat for protecting the photoresist surface from an immersion fluid such as water as a countermeasure for these various problems (Non-Patent Document 1). The top coat in this case is known to be applied with a perfluorinated solvent (completely fluorinated solvent) or to be applied after dissolving a fluorinated resin containing a fluorine-containing carbinol in an organic solvent containing no fluorine atom.
At the application of a top coat to a photoresist, it is necessary to prevent erosion of the lower-layer photoresist surface at the coating. For the purpose, it is extremely important to select a solvent to be used at the application of the top coat composition. Moreover, as methods for peeling the top coat, there have been reported two methods, i.e., a method for dissolution and peeling with a conventional alkaline developing fluid for photoresists and a method for removal with a special fluorine-containing organic solvent (Non-Patent Document 2).
In general, in the case that the immersion fluid is water, purposes of the polymer protective films are the following two, i.e., a purpose of preventing dissolution of chemical substance(s) from the resist into water and a purpose of preventing penetration of water into the resist. When water penetrates into the underlying photoresist, it is reported that the penetration results in appearance of defects in a resist pattern (Non-Patent Documents 3 and 4).
Furthermore, in a display field, development of large-sized flat displays has been promoted and not only uses for personal computers but also uses for televisions have rapidly expanded. As a result, the market of sophisticated films wherein surface flickering and reflection of sunlight and fluorescent light are reduced is increasingly expanding.
[Non-Patent Document 1] Resist and Cover Material Investigation for Immersion Lithography, 2nd Immersion Work Shop, Jul. 11, 2003
[Non-Patent Document 2] S. Kishimura, et al., Impact of Water and Top-coats on Lithographic Performance in 193-nm Immersion Lithography, Proc. of SPIE, Vol. 5753 (2005), p. 20.
[Non-Patent Document 3] Ralph R. Dammel, et al., Leaching Phenomena and their Suppression in 193 nm Immersion Lithography, J. Photopolymer Sci. and Tech., Vol. 18 (2005), p. 593
[Non-Patent Document 4] M. Maenhoudt, et al., Opportunities and Challenges in Immersion Lithography, J. Photopolymer Sci. and Tech., Vol. 18 (2005), p. 571